Estimating motion of wheeled carts

Abstract

Examples of systems and methods for locating movable objects such as carts (e.g., shopping carts) are disclosed. Such systems and methods can use dead reckoning techniques to estimate the current position of the movable object. Various techniques for improving accuracy of position estimates are disclosed, including compensation for various error sources involving the use of magnetometer and accelerometer, and using vibration analysis to derive wheel rotation rates. Also disclosed are various techniques to utilize characteristics of the operating environment in conjunction with or in lieu of dead reckoning techniques, including characteristic of environment such as ground texture, availability of signals from radio frequency (RF) transmitters including precision fix sources. Such systems and methods can be applied in both indoor and outdoor settings and in retail or warehouse settings.

What is claimed is: 
     
       1. A system for monitoring movement of a human-propelled cart, comprising:
 a vibration sensor that attaches to the human-propelled cart and generates vibration data reflective of vibration of the human-propelled cart as the human-propelled cart travels over a surface; 
 a rotation detector that detects rotation of a first wheel of the human-propelled cart and generates rotation data reflective of a rotation rate of the first wheel; and 
 a processing system comprising a hardware processor programmed with executable program code, the processing system programmed to at least:
 determine a rotation rate of the first wheel based on the rotation data; 
 estimate a rotation rate of at least a second wheel of the human-propelled cart at least partly by analyzing the vibration data; and 
 determine a contact status of the first wheel with said surface at least partly by comparing the determined rotation rate of the first wheel to the estimated rotation rate. 
 
 
     
     
       2. The system of  claim 1 , wherein the processing system is further programmed to use the determined rotation rate to estimate a speed of the human-propelled cart. 
     
     
       3. The system of  claim 1 , wherein the processing system is further programmed to, use the estimated rotation rate to estimate a speed of the human-propelled cart. 
     
     
       4. The system of  claim 3 , wherein the processing system is further programmed to use the estimated speed of the human-propelled cart, in combination with cart heading data, to estimate a location of the human-propelled cart. 
     
     
       5. The system of  claim 1 , wherein the processing system is programmed to estimate the rotation rate of at least the second wheel by a process that comprises:
 determining a first peak in a spectrum of the vibration data; and 
 determining a rotation rate that is a harmonic frequency of the first peak. 
 
     
     
       6. The system of  claim 1 , wherein the vibration sensor is a multi-axis vibration sensor. 
     
     
       7. The system of  claim 1 , wherein the vibration sensor is a three-axis accelerometer. 
     
     
       8. The system of  claim 1 , wherein the vibration sensor is mounted to a portion of the cart that is separate from each wheel of the cart. 
     
     
       9. The system of  claim 1 , wherein the vibration sensor is mounted to a handle of the cart. 
     
     
       10. The system of  claim 1 , wherein the processing system is programmed to detect multiple spectral peaks in the vibration data and to determine which of the spectral peaks corresponds to the rotation rate of the second wheel. 
     
     
       11. A method of monitoring movement of a human-propelled cart, comprising:
 generating, with a vibration sensor attached to the human-propelled cart, vibration data reflective of vibration of the human-propelled cart as the human-propelled cart travels over a surface, the vibration data comprising a horizontal component, said human-propelled cart having a plurality of wheels, including a first wheel that comprises a rotation detector; 
 determining a rotation rate of the first wheel based on an output of the rotation detector; and 
 determining, by a hardware processor, whether the rotation rate is consistent with the vibration data at least partly by:
 generating an estimated wheel rotation rate of at least a second wheel of the human-propelled cart at least partly by analyzing the vibration data; and 
 comparing the determined rotation rate of the first wheel to the estimated wheel rotation rate of at least the second wheel. 
 
 
     
     
       12. The method of  claim 11 , further comprising using the determined rotation rate to estimate a speed of the human-propelled cart. 
     
     
       13. The method of  claim 11 , wherein the vibration sensor is an accelerometer that measures acceleration, and wherein determining whether the rotation rate is consistent with the vibration data comprises determining whether a change in the rotation rate of the first wheel is consistent with cart acceleration measured by the accelerometer. 
     
     
       14. The method of  claim 11 , further comprising using the estimated wheel rotation rate to estimate a speed of the human-propelled cart. 
     
     
       15. The method of  claim 14 , further comprising using the estimated speed of the human-propelled cart, in combination with cart heading data, to estimate a location of the human-propelled cart. 
     
     
       16. The method of  claim 11 , wherein determining whether the rotation rate is consistent with the vibration data further comprises identifying multiple spectral peaks in the vibration data and determining that at least one of the spectral peaks corresponds to the rotation rate. 
     
     
       17. The method of  claim 11 , wherein the vibration sensor is mounted to a handle of the cart. 
     
     
       18. A system for monitoring movement of a human-propelled cart, comprising:
 a vibration sensor that attaches to the human-propelled cart and generates vibration data reflective of vibration of the human-propelled cart as the human-propelled cart travels over a surface; 
 a rotation detector that detects rotation of a first wheel of the human-propelled cart and generates rotation data reflective of a rotation rate of the first wheel; and 
 a processing system comprising a hardware processor programmed with executable program code, the processing system programmed to at least:
 determine a rotation rate of the first wheel based on the rotation data; 
 determine whether the first wheel has lost contact with the surface at least partly by determining whether the rotation rate is consistent with the vibration data; and 
 use, in response to determining that the first wheel has lost contact with the surface, the vibration data to generate an estimated wheel rotation rate of at least a second wheel of the human-propelled cart. 
 
 
     
     
       19. The system of  claim 18 , wherein the vibration sensor is an accelerometer that measures acceleration, and wherein the processing system is programmed to determine whether a change in a rotation rate of the first wheel is consistent with cart acceleration measured by the accelerometer. 
     
     
       20. The system of  claim 18 , wherein the vibration sensor is mounted to a handle of the cart. 
     
     
       21. The system of  claim 18 , wherein the processing system is further programmed to use the estimated wheel rotation rate to determine a speed of the human-propelled cart. 
     
     
       22. A method of monitoring movement of a human-propelled cart, comprising:
 generating, with a vibration sensor attached to the human-propelled cart, vibration data reflective of vibration of the human-propelled cart as the human-propelled cart travels over a surface, the vibration data comprising a horizontal component, said human-propelled cart having a plurality of wheels, including a first wheel that comprises a rotation detector; 
 determining a rotation rate of the first wheel based on an output of the rotation detector; and 
 determining, by a hardware processor, whether the rotation rate is consistent with the vibration data, wherein determining whether the rotation rate is consistent with the vibration data comprises:
 identifying multiple spectral peaks in the vibration data; and 
 determining that at least one of the spectral peaks corresponds to the rotation rate.